Since the discovery of polymerase chain reaction (PCR) in 1985, several methods have been developed to achieve nucleic acid amplification, and are currently used in various fields including clinical diagnosis and life science research. Thus, a wealth of information has accumulated regarding nucleic acid‑related enzymes. In this review, some nucleic acid‑related enzymes were selected and the recent advances in their modification along with their application to nucleic acid amplification were described. The discussion also focused on optimization of the corresponding reaction conditions. Using newly developed enzymes under well‑optimized reaction conditions, the sensitivity, specificity, and fidelity of nucleic acid tests can be improved successfully.